In situ combustion production method

ABSTRACT

An improved in situ combustion production method wherein the combustion zone is established within the upper portion of the producing formation and fluids are produced from the formation in such a manner as to maintain the combustion gases within the formation.

United States Patent William B. Ilumpkin Primary Examiner- Ian A. Calvert Attorney-Young and Quigg IN SITU COMBUSTION PRODUCTION METHOD ABSTRACT: An improved in situ combustion production 5 Cl l D i Fi films raw ng g method wherein the combustion zone is established within the U.S. Cl 166/256 u er ortion of the producing formation and fluids are Cl r 4 /24 W 7 produced from the formation in such a manner as to maintain Field of Search 166/256-262 h combustion gases within the formation.

PATENTED SEP28 ISTI 2 v Rpm E INVENTORS W. B. LUM PK I N R. F. MELDAU IN SITU COMBUSTION PRODUCTION METHOD This invention relates to an improved in situ combustion production method. In another aspect, this invention relates to an improved in situ combustion production method for hydrocarbon-containing formations having areas of relatively low vertical permeability.

In heretofore utilized in situ combustion production methods, a combustion front is established within a hydrocarbon-containing formation adjacent an injection well. After the combustion zone is established, oxidant is continuously delivered to that zone to support combustion of the in-place hydrocarbons. Combusting the hydrocarbon generates large volumes of combustion gases which force the in-place hydrocarbons through the formation to a distant production well. The combustion zone and openings from the formation into the production well generally extend across the entire thickness of the formation. The combustion zone, in time, moves from the injection well thereby sweeping hydrocarbons through the entire formation thickness toward the producing well. Other methods generate a combustion zone through various portions of the producing formation. In these methods, however, the gases from combustion that function as the driving force for the in-place hydrocarbons are produced upon reaching and entering the production well. This production of combustion gases lowers the formation pressure, requires a great deal of equipment and power to treat, compress, and reinject the produced combustion gases and cause the producing equipment to often malfunction and operate inefficiently.

It is therefore an object of this invention to provide an improved in situ combustion production method. Another object of this invention is to provide an improved in situ combustion production method for formations having areas of relatively low vertical permeability adjacent the production well. Yet another object of this invention is to provide an in situ combustion productionmethod that maintains relatively high formation pressures. A further object of this invention is to provide an improved in situ combustion production method that requires less equipment, supervision and power and operates more efficiently. Other aspects, objects, and advantages of the present invention will becomeapparent from astudy of the disclosure, the appended claims, and the drawing.

The drawing is a diagrammatic sketch of injection and production wells penetrating a hydrocarbon formation being produced by the improved in situ combustion production method of this invention.

ln the drawing, at least one injection well 2 and one or more production wells 4 extend from the surface of the ground 6 downwardly through a subterranean hydrocarbon-containing formation 8. The formation 8 generally has overlying and underlying relatively impervious layers 10 that confine the hydrocarbons within their respective formation 8. The wells 2, 4 are spaced a distance from one another. it is recommended that the hydrocarbon-containing formation 8 that is to be produced by the method of this invention have discontinuous areas of relatively low permeability l 1, such as shale stringers, extending through the formation outwardly from the producing well bore. Formations 8 with high continuous vertical permeabilities near the producing well allow the combustion gases to channel downwardly through the formation with resultant combustion gas coning into the production wells 4, bypassing of in-place hydrocarbons, and the absence of an effectively established upper zone of elevated pressure. It is also preferred that the wells 2, 4 utilized in this invention have casing 12 that is cemented or affixed to the hydrocarbon-containing formation 8 in a manner to form a fluid tight seal in the annular space between the outer surface of the casing and the adjacent formation 8. To those skilled in the art, this type completion is commonly referred to as being set through and cemented".

In the method of this invention, the injection well 2 or wells are opened into communication with the upper portion 14 of the hydrocarbon-containing formation. Where the well 2 is completed by setting through and cementing, the opening is made by notching the casing or cutting the casing with abrasives, jet charges, bullets, or the like. If the well 2 is an open hole completion, i.e., having no cemented casing through the hydrocarbon-containing formation, a formation packer can be set in the formation to restrict communication between the formation 8 and the well bore to the upper portion of said formation 8. It is also preferred that the openings 18 or perforations into the upper portion 14 of the formation 8 extend over a length of not greater than 25 percent of the thickness of the hydrocarbon-containing formation as measured from the top of the formation '8 downwardly. lf openings 18 are formed in the injection wells 2 to a greater depth relative to the top of the formation, the efficiency of the production method of this invention is decreased owing to the utilization of energy required to move the hydrocarbons through the formation 8.

Remotely located production wells 4 are opened into communication with the lower portion 16 of the hydrocarbon-com taining 8 in the manner described above. The openings 18 into the lower portion 14 of the formation 8 should be over not more than 50 percent of the formation as measured from the bottom of the formation 8 upwardly in order to reduce gas coning without unduly limiting production rates.

In situ combustion within the hydrocarbon-containing formation 8 is thereafter established in the upper portion of the formation adjacent the injection well 2. Oxidant, preferably air, is thereafter injected downwardly through the injection well 2 and into the upper portion 14 of the formation 8 to advance the combustion zone 20 through the formation 8. The pressure within the production wells 4 is lowered and hydrocarbons entering the production wells 4 from the hydrocarbon-containing formation 8 through the openings 18 adjacent the lower portion 16 of said formation 8 are produced to the surface and recovered. it is important that the production wells 4 be produced at a rate at which coning of combustion gas is minimized and combustion gases are substantially not produced through the production wells 4 to the surface but are substantially all maintained within the formation 8.

The production wells 4 can also be opened into communication with both the upper and lower portions 14, 16 of the hydrocarbon-containing formation. In production wells 4 having both upper and lower portions 14, 16 opened, hydrocar bons flow from the formation 8 through both upper and lower openings 18 and are produced to the surface. Where upper portions of the formation are opened into the production well 4, fluids are produced from the well 4 only until combustion gases from the combustion zone 20 enter and are produced by the production well 4. Immediately after the breakthrough of any combustion gases into the production well 4, the openings 18 adjacent the upper portion 14 of the formation 8 in that particular well 4 are closed and production from the formation 8 is limited to fluids entering the production well 4 only through openings 18 adjacent the lower portion 16 of said formation 8 as described above. Production packers 17 can be utilized for controlling the closing and opening of various openings 18 in the production wells 4.

By utilizing openings 18 adjacent the upper portion 14 of the formation 8 for production of fluids only prior to combustion gas breakthrough, the small portion of energy utilized to move hydrocarbons through the formation 8 ahead of the combustion zone 20 is not wasted. Producing the upper portion 14 of the formation 8 also assists in forming a combustion zone 20 extending through the areal extent of the reservoir. Closing of the upper openings 18 in the production wells 4 or, as previously described, producing the production wells 4 from only the lower portion of the formation at controlled rates causes the combustion gases to be retained within the reservoir.

Conduction of in situ operations over the upper portion 14 of the formation 8 and maintaining combustion gases within the reservoir provides a method for maintaining higher reservoir pressures than heretofore utilized production methods. Since the combustion gases are substantially hot produced through the production well 4, the production method of this invention requires less equipment, supervision and power. The efficiency of the in situ combustion method of this invention is also improved relative to heretofore utilized methods owing to the fact that high reservoir pressures are maintained by maintaining the combustion gases within the reservoir. The pressures generated by the combustion gases function to assist gravity drainage of the reservoir, maintain the in-place formation fluid above the bubble point, and prevent water encroachment from watering out the production wells 4.

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion and accompanying drawing, and it should be understood that this invention is not to be unduly limited thereto.

What is claimed is: 1. An improved in situ combustion method for producing hydrocarbons contained within a subterranean formation being penetrated by an injection well and at least one producing well spaced from said injection well and having discontinuous areas of low vertical permeability extending outwardly from the producing well, comprising:

opening the injection well into communication with only the upper portion of the hydrocarbon-containing formation;

opening the production well into communication with the upper and the lower portion of the hydrocarbon-containing formation;

establishing in situ combustion within only the upper portion of the formation adjacent the injection well; advancing the combustion zone through the formation by injecting oxidant downwardly through the injection well and into only the upper portion of the formation; lowering the pressure within the production well;

producing hydrocarbons entering the production well from the hydrocarbon-containing formation through the opening adjacent at least the upper portion of said formation;

closing the opening the producing well adjacent the upper portion of the hydrocarbon-containing formation immediately after combustion gases from the combustion zone are produced by the production well; and

producing hydrocarbons entering the production well only through openings adjacent the lower portion of the hydrocarbon-containing formation at a rate sufficiently low to substantially prevent combustion gas coning and entering the production well to maintain substantially all combustion gases within the formation.

2. A method, as set forth in claim 1, wherein the upper portion of the formation is opened into the injection well over not more than the uppermost 25 percent of the thickness of the formation at said injection well.

3. A method, as set forth in claim 1, wherein the lower portion of the formation is opened into the production wells over not more than the lowermost 50 percent of the thickness of the formation at said production wells and the upper portion of the formation is opened into production and injection wells over not more than the uppermost 25 percent of the thickness of the formation at said production and injection wells.

4. A method, as set forth in claim 1, wherein the oxidant is air.

5. A method, as set forth in claim 1, further including producing hydrocarbons entering the production well only through openings adjacent the lower portion of the hydrocarbon-containing formation at a rate sufficiently low to substantially prevent water encroachment into the production well. 

2. A method, as set forth in claim 1, wherein the upper portion of the formation is opened into the injection well over not more than the uppermost 25 percent of the thickness of the formation at said injection well.
 3. A method, as set forth in claim 1, wherein the lower portion of the formation is opened into the production wells over not more than the lowermost 50 percent of the thickness of the formation at said production wells and the upper portion of the formation is opened into production and injection wells over not more than the uppermost 25 percent of the thickness of the formation at said production and injection wells.
 4. A method, as set forth in claim 1, wherein the oxidant is air.
 5. A method, as set forth in claim 1, further including producing hydrocarbons entering the production well only through openings adjacent the lower portion of the hydrocarbon-containing formation at a rate sufficiently low to substantially prevent water encroachment into the production well. 